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B Roscherr, P S Coppi (Yale University)
A significant fraction of the power emitted by blazars in the TeV energy range should be attenuated by photon-photon pair production with background light. The ensuing electromagnetic cascade upscatters microwave background photons, and as a result the initial TeV radiation emerges as photons of lower energy. The angular and time dependence of the observed cascade spectrum is very sensitive to the strength of the intervening intergalactic magnetic field (IGMF). We calculate the time dependent cascade spectrum expected from TeV flares in Mrk 501 and derive the implied constraints on the IGMF strength. We also calculate the cascade spectrum from blazars at higher redshifts. Cascades from these sources would be more developed, resulting in a higher yield of low energy photons, in particular, X-rays. We explore the possibility of AXAF resolving an X-ray halo from these sources, and thereby providing a constraint on the IGMF strength on cosmological distance scales.
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